Observations of a Radio-quiet Solar Preflare

The preflare phase of the flare SOL2011-08-09T03:52 is unique in its long duration, its coverage by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Nobeyama Radioheliograph, and the presence of three well-developed soft X-ray (SXR) peaks. No hard X-rays (HXR) are observed in the preflare phase. Here we report that also no associated radio emission at 17 GHz was found despite the higher sensitivity of the radio instrument. The ratio between the SXR peaks and the upper limit of the radio peaks is larger by more than one order of magnitude compared to regular flares. The result suggests that the ratio between acceleration and heating in the preflare phase was different than in regular flares. Acceleration to relativistic energies, if any, occurred with lower efficiency.Comment: 9 pages, 3 figures, accepted by Solar Physic

Un\u2019indagine sperimentale sul ruolo della temperatura am- biente nel processo di riscaldamento/raffreddamento per ir- raggiamento

The process of heating / cooling of an object in vacuum can be studied by the known Stefan's law. Many studies have investigated this phenomenon without inquire the role of the environment and of its temperature. In this paper the author proposes an experimental method through which to study the above process, by monitoring the ambient temperature on the assumption that this can vary with an exponential law. Under this hypothesis, in defined conditions, the temporal evolution of cooling of the object is similar to the case where the con- vection and / or the conduction are the principale phenomenon of energy exchange

Charged Higgs-boson production in association with an electron and a neutrino at electron-positron colliders

We present results of a calculation of the cross section for the production of a charged Higgs boson in association with an electron and a neutrino at electron-positron colliders (e+ e- -> H+ e- nu_e-bar, H- e+ nu_e). We study predictions for the cross section in the Minimal Supersymmetric Standard Model (MSSM) and the Two Higgs Doublet Model (THDM), highlighting possible differences. The process is effectively loop-induced in both models. Hence, the cross section is expected to be strongly model-dependent. Most notably, due to the presence of superpartners, the MSSM amplitude contains Feynman graphs of pentagon-type, which are not present in the THDM. This is the first complete one-loop calculation of the cross section for this process in the THDM and the MSSM. For both models, so far, only approximate results with limited ranges of validity were available. Our main aim here is to clarify several open questions in the existing literature on this process. Specifically, we will discuss the validity of the Heavy Fermion loop approximation in both models, and of the Fermion/Sfermion loop approximation in the MSSM.Comment: 21 pages, 8 figures, 1 tabl

Observational evidence for return currents in solar flare loops

Context: The common flare scenario comprises an acceleration site in the corona and particle transport to the chromosphere. Using satellites available to date it has become possible to distinguish between the two processes of acceleration and transport, and study the particle propagation in flare loops in detail, as well as complete comparisons with theoretical predictions. Aims: We complete a quantitative comparison between flare hard X-ray spectra observed by RHESSI and theoretical predictions. This enables acceleration to be distinguished from transport and the nature of transport effects to be explored. Methods: Data acquired by the RHESSI satellite were analyzed using full sun spectroscopy as well as imaging spectroscopy methods. Coronal source and footpoint spectra of well observed limb events were analyzed and quantitatively compared to theoretical predictions. New concepts are introduced to existing models to resolve discrepancies between observations and predictions. Results: The standard thin-thick target solar flare model cannot explain the observations of all events. In the events presented here, propagation effects in the form of non-collisional energy loss are of importance to explain the observations. We demonstrate that those energy losses can be interpreted in terms of an electric field in the flare loop. One event seems consistent with particle propagation or acceleration in lower than average density in the coronal source. Conclusions: We find observational evidence for an electric field in flare loops caused by return currents.Comment: A&A, in pres

A mesoscopic mechanical model of the surface tension and some simulation results

Drops of mercury do not spread on a surface. A metal paper clip can float on water. These phenomena are macroscopic manifestations of molecular interactions and can be explained in terms of surface tension. In this study, we discuss a simple mesoscopic mechanical model of the surface tension and the results of numerical fluid dynamics simulations implemented on the basis of it. We study the droplet formation without and with gravity when it can drop from a narrow hole like a trickling tap and finally the behaviour of free surface liquid in a vessel. Teachers and students can be able to study the surface tension by using the computer simulation as a "tool" for analysing and discussing the droplet and the liquid behaviour in several different conditions

Quantitative and qualitative analysis of the mental models deployed by undergraduate students in explaining thermally activated phenomena

In this contribution we describe a research aimed at pointing out the quality of mental models undergraduate engineering students deploy when asked to create explanations for phenomena/processes and/or use a given model in the same context. Student responses to a specially designed written questionnaire are initially analyzed using researcher-generated categories of reasoning, based on the Physics Education Research literature on student understanding of the relevant physics content. The inferred students\u2019 mental models about the analyzed phenomena are categorized as practical, descriptive, or explanatory, based on an analysis of student responses to the questionnaire. A qualitative analysis of interviews conducted with students after the questionnaire administration is also used to deepen some aspects which emerged from the quantitative analysis and validate the results obtained

Where to find a dark matter sterile neutrino?

We propose a strategy of how to look for dark matter (DM) particles possessing a radiative decay channel and derive constraints on their parameters from observations of X-rays from our own Galaxy and its dwarf satellites. When applied to the sterile neutrinos in keV mass range, it allows a significant improvement of restrictions to its parameters, as compared with previous works.Comment: 5 pp, revtex; v3: 1-sigma limits have been replaced by more conservative 3-sigma limits, a picture illustrating the data analysis methods has been ade

The Calcium Triplet metallicity calibration for galactic bulge stars

We present a new calibration of the Calcium II Triplet equivalent widths versus [Fe/H], constructed upon K giant stars in the Galactic bulge. This calibration will be used to derive iron abundances for the targets of the GIBS survey, and in general it is especially suited for solar and supersolar metallicity giants, typical of external massive galaxies. About 150 bulge K giants were observed with the GIRAFFE spectrograph at VLT, both at resolution R~20,000 and at R~6,000. In the first case, the spectra allowed us to perform direct determination of Fe abundances from several unblended Fe lines, deriving what we call here high resolution [Fe/H] measurements. The low resolution spectra allowed us to measure equivalent widths of the two strongest lines of the near infrared Calcium II triplet at 8542 and 8662 A. By comparing the two measurements we derived a relation between Calcium equivalent widths and [Fe/H] that is linear over the metallicity range probed here, -1<[Fe/H]<+0.7. By adding a small second order correction, based on literature globular cluster data, we derived the unique calibration equation [Fe/H]$_{CaT} = -3.150 + 0.432W' + 0.006W'^2$, with a rms dispersion of 0.197 dex, valid across the whole metallicity range -2.3<[Fe/H]<+0.7.Comment: Accepted for publication in A&

Relationship between mild to moderate renal dysfunction and obstructive sleep apnea: Data from the European sleep apnea database

The relationship between severity of obstructive sleep apnea (OSA) and kidney function was investigated in the European Sleep Apnea Database (ESADA), where clinical, sleep, and biochemical data of patients studied for suspected OSA in 24 sleep centres of 17 European countries are stored. After excluding patients with missing data or extremely high/low creatinine values, data from 8112 subjects (2328 female) with creatinine values ranging between 0.5 and 2.0 mg% were analyzed. Estimated glomerular filtration rate (eGFR) was obtained with the Modified Diet in Renal Disease (MDRD) equation. Patients were subdivided into two groups: group 1 (n = 3709) studied by full polysomnography; group 2 (n = 4403) studied by nocturnal cardiorespiratory monitoring. Altogether, 8.5% subjects had an eGFR<60 ml/min/1.73m2. At univariate analysis, eGFR correlated to age, comorbidities and severity of OSA in both groups. At logistic regression analysis, risk factors for eGFR<60 were in group 1: diabetes, female gender, age, body mass index, and lowest nocturnal SaO2 (r2=0.086); in group 2: hypertension, female gender, age, and lowest nocturnal SaO2 (r2=0.087). In conclusion, as expected, comorbidities, female gender and advanced age are significant risk factors for low eGFR in subjects with OSA. While traditional severity measures of OSA (apnea/hypopnea index, oxygen desaturation index) did not contribute to low eGFR, more severe nocturnal hypoxia captured by lowest nocturnal SaO2 appeared as a significant predictor in this large patient cohort. The ESADA study is supported by ResMed and Philips Respironics

Evaluation of radar multiple scattering effects in Cloudsat configuration

International audienceMonteCarlo simulations have been performed to evaluate the importance of multiple scattering effects in co- and cross-polar radar returns for 94 GHz radars in Cloudsat and airborne configurations. Thousands of vertically structured profiles derived from some different cloud resolving models are used as a test-bed. Mie theory is used to derive the single scattering properties of the atmospheric hydrometeors. Multiple scattering effects in the co-polar channel (reflectivity enhancement) are particularly elusive, especially in airborne configuration. They can be quite consistent in satellite configurations, like CloudSat, especially in regions of high attenuation and in the presence of highly forward scattering layers associated with snow and graupel particles. When the cross polar returns are analysed [but note that CloudSat does not measure any linear depolarization ratio (LDR hereafter)], high LDR values appear both in space and in airborne configurations. The LDR signatures are footprints of multiple scattering effects; although depolarization values as high as ?5 dB can be generated including non-spherical particles in single scattering modelling, multiple scattering computations can produce values close to complete depolarization (i.e. LDR=0 dB). Our simulated LDR profiles from an air-borne platform well reproduce, in a simple frame, some experimental observations collected during the Wakasa Bay experiment. Since LDR instrumental uncertainties were not positively accounted for during that experiment, more focused campaigns with air-borne polarimetric radar are recommended. Multiple scattering effects can be important for CloudSat applications like rainfall and snowfall retrievals since single scattering based algorithms will be otherwise burdened by positive biases